The Tohono O’odham who are native to southern Arizona looked at the mountain chain lying to the north of what is now Tucson and thought that it resembled one of the green toads that shared the Sonoran Desert with them.

They called the sierra Babad Do’ag (“Frog Mountain”), and if you look at the mass of volcanic rock that rises 9,157 feet (2,791 meters) above sea level like a huge island out of the desert, you might detect some resemblance, if in nothing else than the mountains’ rumpled skin.

The Jesuit explorer Eusebio Francisco Kino is believed to have bestowed the name Sierra Santa Catarina in April 1697, and by the 1880s, the people of Tucson were calling the range the Santa Catalina Mountains. All the while, O’odham, Spanish, Mexican, and Anglo people entered the jagged sierra, whose ancient, much-metamorphosed volcanic core is laced with streamlined canyons that nourish animal and plant life.

Pusch Ridge, on the western edge of the range, rises above one such canyon. Historically, it was long home to a population of bighorn sheep, as well as numerous deer. For that reason, and by virtue of its comparative ease of access, hunters often climbed the ridge to bag game, whose population remained relatively steady until the 1970s.

It was during that decade, a time of double-digit growth, that things began to change for the worse, at least from a bighorn’s point of view. Housing developments began to climb the ridge, busy roads girded the mountains on all sides, and metropolitan Tucson’s population began its rise from the 250,000 of 1975 to the million-plus of today.

Sensitive to the presence of humans, the bighorn population, probably never numbering more than a hundred or so individuals, began to decline, steadily and inexorably. Finally, toward the end of the 1980s, travelers into the western edge of the mountains realized that the bighorns had disappeared. Apart from a few scattered skulls near watering holes, it was as if they had never been there in the first place.

Fast-forward to 2013. Well-meaning game officials, federal and state, had for some time been discussing the possibility of reintroducing bighorn sheep into the mountains. Now, on November 18, a small herd, captured in the western desert, was released into the mountains: 24 ewes, six rams, one lamb. According to Arizona Game & Fish officials, that herd represented the first phase of an injection, so to speak, of bighorns intended to bring the population in the Santa Catalinas back to about 100 individuals.

But then the law of unintended consequences began to exert its force.

Unintended, but not unforeseeable. In 2000, federal game officials undertook an aerial survey of the Kofa National Wildlife Refuge, near where the Santa Catalina returnee herd was taken 13 years later. From the air, rangers spotted “what looked like three golden retrievers,” as they reported. Those animals were mountain lions, which were all but unknown in the low desert country. They, too, were on the move, displaced by development in the mountains of southern Arizona, and they found a bonanza in the Kofas. There the bighorn population was about 800 in 2000, 620 in 2003, and 390 in 2006. It was about 400 at the last census, a decline that can be traced to a flourishing population of predators.

Just so, by November 29, one of the Santa Catalina sheep was dead, killed by mountain lions, whose population had in the meantime stabilized and then grown in the high mountains, at least in part owing to the ready presence of prey in the form of household pets on the slopes below. A few days later, the corpse of another sheep was found. By the end of the year, four sheep, one of them pregnant, had been killed, and several others had fallen off the radar.

Game officials responded with a heavy-handedness that longtime animal control critics could predict: they sent trackers into the mountains and killed two mountain lions. Game & Fish had anticipated the need to do just that, though no official had ventured any notion of just how much control was going to be permitted: Would five mountain lions be killed, and then no more? How many lions would have to die was a question left unanswered.

In any event, the move excited considerable controversy in Tucson, and animal welfare activists demanded that Game & Fish immediately call a halt to such killings on the grounds that the lions, after all, are just doing what mountain lions do, substituting sheep for their preferred deer, skunks, and other prey.

Those officials are now faced with difficult choices. One is to track the fortunes of the sheep population without adding to it in an effort to determine just how many predators are up in the high country. Another is to add captured individuals to the population, a move that might well turn out to be a real-life example of the proverbial lambs to the slaughter if that population is large.

For the time being, the remaining sheep have begun to relocate themselves from the lower canyons of the mountains, places full of dense vegetation that affords predators ample places to hide, and up to higher, bare slopes that offer a better lookout for trouble.

And for the time being as well, this question remains: When an animal population absents itself from a place, in whose interest is it to restore it? The unfolding fate of the Santa Catalina bighorns will have a bearing on that conversation.

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